A Study Of Project Method For Load Bearing Structure Fatigue Strength In Power Vehicle

This thesis inseparably combines the design features for lightening the load bearing structure of high speed power vehicle and the crying need of the vehicle manufacturer that requires for the project method of load bearing structure fatigue strength analysis. The lightening design of load bearing structure, the structure dynamic optimizing design, the project method for the fatigue strength evaluation, and the lateral stiffness and its stability of composite spring suspension system evaluation were discussed.Under the multidirectional loading affect, according to the features that the stress distribution of vehicle's load bearing structure is usually situational in the multiaxial stress state, raises the suitable methods that change the multiaxial stress of evaluating the fatigue strength of vehicle's load bearing structure to the uniaxial stress one, they are the ORE Method and the DIN 15018 Method. By using the revised Goodman fatigue curve or Moore—Kommers— Japer fatigue curve evaluates the fatigue strength of vehicle's load bearing structure, and develops the suitable analysis software for evaluating the fatigue strength of vehicle's load bearing structure.Based on the UIC and EN standards, in order to suit these standards about the vehicle's load bearing structure design and its strength test, the fatigue strength of high speed power vehicle's body, frame, wheelset axle and wheel, etc. were analyzed, a project method for analyzing the fatigue strength of load bearing structure was advanced. According to the loading spectrum used for the fatigue strength of load bearing structure, grades the testing load on the basis of the rain flow counting method and gets the stress distribution of the structure in every grade of load by using the finite elements method. According to the symmetrical cyclic S—N curve that the material or structure parts show under the nominated life, the thesis evaluates the fatigue strength or nominated life for the frame, and gives theoretical basis to the fatigue design of the new product.Based on the classic analysis theory that simplifying cylinder helical compressed spring to the Timoshenko Beam, the thesis combines the testing result of the lateral stiffness and stability for flexicoil spring and cylinder helical compressed spring with less number of active coils in spring, revises the counting height that greatly influences the lateral stiffness of spring and raises the effective method to compute the lateral stiffness of vehicle's primary andsecondary suspension. According to the characteristic of flexicoil spring suspension system that our vehicle have, the thesis guides the direct solve for calculating the lateral stiffness by adding the round or rotary rubber cushion structure at one or both sides of flexicoil spring and round rubber structure system at one side or both sides of parallel flexicoil spring for the first time. Based on the tenet that composite spring system instability and stability theory of compressed column, the paper raises an evaluating method to the stability of composite spring system— Stiffness Method, reasonably combines the analysis method of the lateral stiffness and the stability of spring system, so solves the theoretical analysis for this kind of issues effectively. The testing results verify the correctness for the theoretical analysis method. By using the elastic dynamics analysis, the results reflect the nonlinear peculiarity to the lateral stiffness of suspension system.Because of the remarkable characteristic that forced frequency range of high speed train's rail-wheel system is spacious, the paper puts the wheelset axle and the track of rail vehicle system to elasticity, simplifies the wheel and axle-box to the collective quality and the moment of inertia, and sets up a continuous elasticity model of the wheelset axle by using Timoshenko Beam. To get the figures of natural frequency and vibration modes of non-uniform Temoshenko Beam by using the transfer matrixes method and the generalized coordinates for the wheelset axle, according to the quadrature of vibration mode function, gets the coupled systems of second order differential equation for the wheelset axle vibration mode coordinate, sets up the wheel-track elasticity coupling dynamics model, analyses the effects that the wheelset axle dynamic stiffness and the axle vibration specificity gives to the wheel/rail force, the wheelset axle's selves vibration characteristic and the wheelset axle stress, forecasts the fatigue strength of wheelset axle under the loading function occasionally. The result of theoretical analysis points out that, by improving the dynamic stiffness of lightening wheelset axle is beneficial to lowering the wheel/rail dynamic force and raising the wheelset axle's fatigue life.